Method and apparatus for producing seamless retroreflective sheeting

ABSTRACT

A method and apparatus for forming &#34;seamless&#34; retroreflective sheeting is described. At least two mold surfaces are used, each having alternate areas of arrays of prism recesses and spaces. In a first step, prisms are formed in one of the mold surfaces and applied to a base film or web. Next, prisms are formed on the second mold surface and applied to the spaced areas left in the first step.

RELATED APPLICATION

This application is a division of application Ser. No. 08/444,759 filedMay 19, 1995, now U.S. Pat. No. 5,558,740, which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

A demand exists for retroreflective materials i.e., materials capable ofreflecting the predominant portion of light rays impinging thereon in asubstantially parallel path toward the source of the light. Aparticularly efficient type of retroreflective element employs moldedmembers of cube-corner formations for retroreflective structures.

Cube-corner reflectors molded from glass and more recently from acrylicresins have commonly been employed as safety devices on bicycles,automobiles and other vehicles.

Rowland in U.S. Pat. No. 3,689,346 describes a process in whichretroreflective sheeting is produced on a continuous basis by applyingtransparent sheet material over a hardenable molding material previouslydeposited upon a moving mold surface, after which the molding materialis solidified and bonded to the sheet material to produce a compositestructure. The mold surface has an array of minute, contiguouscube-corner recesses therein, so that the sheeting correspondingly has amultiplicity of closely spaced cube-corner formations spaced about andprojecting form a smooth surface of the sheet material, which providesthe body portion thereof.

Currently, masters for the molds are flycut using machinery which mustbe accurate to approximately one millionth of an inch over the entiresize of the master. Machines of this type can be used to make masterswhich are as large as 12"×12" but not much larger. The larger the sizeof the machine, the greater the cost. A machine that can flycut a12"×12" master costs approximately $500,000 and a machine that willflycut a 18"×18" master costs approximately $1,000,000. The costincreases exponentially with the machine size because of the accuraciesrequired. Typically, electroformed replicas of the master are made andthe replicas are assembled into larger molds using two steps.

The first step is to finish the edges of the 12"×12" pieces using a veryprecise edge finishing process, such as lapping and polishing or flycutting. Three 12"×12" pieces are then assembled into a roughly 12"×36"mold. The 12" long seams which are made are less than 0.001" in widthand are acceptable for most applications and also the replica of theassembly is one continuous electroform. Strength at the seams is not aproblem because the piece is all one electroformed piece of metal. Thenext step is to assemble the 12"×36" molds to one another to form abelt. This step requires edge finishing equipment which must beextremely precise over the entire 36" width of the mold. It is possibleto assemble larger molds at this point, for example, a 24"×36" mold or a36"×36" mold, but the equipment required to edge finish and also theequipment needed to electroform larger parts, becomes more sophisticatedand much more expensive.

Therefore it is typically preferred to weld the 12"×36" molds togetherand, to achieve the strength required for the finished belt, theassembly is welded on both the back and the front of the seams. Thelight weld that is present on the front of the seams is approximately0.015" to 025" wide, will not retroreflect and creates a seam that ismore visible than desired in daylight and in retroreflected light. Thetextured surface of the seam causes scattering of the reflected lightand makes the seam very visible, especially if the material made fromthe molds is metallized.

SUMMARY OF THE INVENTION

Seamless retroreflective sheeting is formed in accordance with thepresent invention. By "seamless" is meant, retroreflective sheetinghaving no seams in the sheeting of a size greater than about 0.010inches over a substantially continuous web of material, as long asseveral thousand feet, so that the "seams" are substantially invisibleto the unassisted human eye from a distance of about 10 feet.

The foregoing is accomplished by providing at least two mold surfaces.Preferably, the mold surfaces are provided on rotatable drums. Each moldsurface contains alternate areas of arrays of prismatic recesses andblank areas of spaces or voids. Preferably the areas are either equal toone another, or the areas of prismatic recesses are slightly larger thanthe areas of spaces. Hardenable, prism forming liquid material, isapplied to a first one of the mold surfaces to fill the areas of prismrecesses and a base film is applied to the liquid filled recessed areas.The material is heated, or otherwise treated, to solidify the materialthereby forming alternate areas of arrays of prisms bonded to the filmand blank areas consisting of spaces or voids.

The film thus formed is transported to the second mold surface where theareas of arrays of prismatic recesses in the second mold surface arefilled with the hardenable prism forming liquid materials and applied tothe film at the blank areas of the film where the spaces remain. Thematerial is then solidified leaving a continuous "seamless" sheet or webof retroreflective prisms formed on the film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrational view of apparatus embodying thepresent invention.

FIG. 2 is a schematic plan view of the drum 10 of station A of FIG. 1 ata given instant in time.

FIG. 3 is a schematic view of the drum 10' of station B of FIG. 1 at alater instant in time.

FIG. 4 is an enlarged plan view of a portion of the mold plate 16 ofFIG. 1.

FIG. 5 is a schematic fragmentary view in partial section to an enlargedscale of the apparatus of FIG. 1.

FIG. 6 is a fragmentary side view of reflective sheeting produced inaccordance with an alternate embodiment of the present method.

FIGS. 7A-C are a series of fragmentary side views of alternate steps inthe process of making retroreflective sheeting in accordance with theinvention.

FIGS. 8A-C are a series of fragmentary side views of steps in analternative process of making retroreflective sheeting in accordancewith the invention.

FIG. 9 is a block diagram of a control system for controllingregistration of the two separately formed prism arrays with respect toone another.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Turning now to FIGS. 1-3 of the appended drawings an apparatus forproducing seamless reflective sheeting on a continuous basis will now bedescribed in detail.

The apparatus includes a pair of molding drums of about 48 inchesdiameter 10,10' mounted upon shafts 12,12' for rotation in the directionindicated by the arrows (i.e. clockwise). Drum A is designated themaster axis and it produces the reference signal for the machinesynchronization. The circumferential portion of the drums 10,10',generally designated by the numerals 14,14', consist of a multiplicityof 10 inch by 30 inch nominally sized metallic plates 16,16' bonded tothe circumferential base portions. Alternate 10 inch plates 70,70' areformed with a multiplicity of identical contiguously arrangedcube-corner recesses or prismatic indentations 22,22' (a portion ofwhich is shown greatly enlarged in FIG. 4).

Note that the dimensions of the mold recesses and hence the resultantprisms forming the array are extremely small. The side edge dimension Dof each prism is a maximum of 0.025 inches and preferably not more than0.010 inches with an optimum size in the order of 0.0005 to 0.008inches. The plates 16, 16' are provided in alternate areas 70, 70' aboutthe circumference of the drums 10, 10' to provide a molding surface thathas a substantially continuous array of cube-corner recesses 22 thereinwith blank areas 72, 72' therebetween which are devoid of recesses.

A coating assembly, generally designated by the numerals 24,24' ismounted adjacent a segment of a respective drum 10,10'. This assemblyconsists of three coating stations, 241, 242, 243 and 241', 242', 243',each one of which will apply a metered amount of the prism formingliquid i.e. resin into the prism recesses. Each station controls theappropriate controls and rollers to precisely deposit the liquid withoutoverfilling the recesses. The three stations are used to enhance theremoval of air from the bottoms of the prismatic plates. A fourthcoating station 244,244', identical to the first three, coats the web 46before it is laminated to the drums 10,10'.

A bank of ultraviolet lights 40,40' is mounted (also by means not shown)adjacent the drums 10'10' for curing of the materials deposited thereonat a point about the axis between the laminating roller 50,50' and thecold air plenum 38,38'.

Rotatably mounted film feed and take-up reels 42 and 44, respectively,are positioned on opposite sides of the assembly. In passing from thefeed reel 42 to the drum 10, the film 46 passes through a tension nip(not shown) and thereafter about a relatively resilient pressure roll50, also referred to as the laminating roll, the latter being mountedwith its surface closely adjacent to that of the drum 10 and with theirrespective axes of rotation parallel. A stripping roll 52 is similarlymounted on the opposite side of the drum 10, and the partially formedreflective sheeting generally designated by the numeral 54, passes aboutit in its travel to the next tension nip 48'. Sheeting 54 travels to thesecond drum 10' where it proceeds through a similar set of devices(designated by the numeral 54, passes about it in its travel to the nexttension nip 48'. Sheeting 54 travels to the second drum 10' where itproceeds through a similar set of devices (designated by a prime suffix)corresponding to those heretofore described in connection with drum 10.An edge trimming station 80,80' is employed after each station to removeany poorly replicated edges from the web 54. The motors 56,56' drive thedrums in a conventional manner, under computer control from controlsystem 100 such as the chains 58,58' provided about the shafts 12,12'and shaft 60,60' thereof.

Operation of the apparatus will be apparent from the foregoing and thefollowing description. As the drum 10 in section A continuously rotates,a hardenable molding material 64,64' in fluid form is depositedthereupon on the prismatic recesses. These coating stations 24,24' areheld in register through the homing sensors 82,82' mounted adjacent thecircumference of the drum 10,10' in a fixed position. The homing sensorsprovide an electrical feedback signal to the control system 100 toadjust the position of the coating stations 24,24'. Film 46 iscontinuously withdrawn from the feed reel 42 and applied first againstthe drum 10 by the laminating roll 50, which cooperates with the drum 10to provide a nip at which the hardenable material 64 is uniformlydistributed over the surface of the prism array recess areas 70 of themolds 16 on drum 10, and at which intimate contact is effected betweenthe material 64 and the film 46.

The freshly applied material 64 and the film 46, travel together pastthe bank of ultraviolet lamps 40, where hardening of the material 64 andbonding thereof to the film 42 are concurrently effected. Thereafter,the cold air plenum 30 helps cool the material so that the partiallycompleted reflective sheeting 54 can be readily stripped from the drum10 about the roll 52.

As shown in the enlarged fragmented simplified schematic side view ofFIG. 5, at this stage of the process, arrays of cube-corner prisms 22have been formed on the film 46 only adjacent areas 70 of the moldsurface 16 while the remaining portions of the film adjacent areas 72are left void. In the next step of the process, the areas on the filmleft with voids are filled in with an array of prisms 22' to form asubstantially seamless continuous length web 73 of cube-cornerformations 22 on the resultant film 54'.

To do this, the plates 16' on drum 10' are arranged on the drum withrespect to the film 54 in such a manner that the prism array recess area70' coincides with the voids 75 left on the film 54' and the blank area72' on the mold surface coincides with the areas 77 on the film 54 wherethe array of prisms 22 were previously formed on drum 10.

Referring back to FIG. 1, the partially completed film 54 is fed througha tension nip 48' and past a registration check optical sensor 90. Thissensor feeds an electrical signal related to the position of theincoming web 54 to the computer system 100 and positional correctionsare processed to ensure that the partially completed reflective film 54is in proper alignment to contact the drum 10' through the laminatingroll 50', where it encounters the freshly applied hardenable material64' on the prism array recess areas 70' of the molds 16' on drive 12';but only at the spaces 72 left on the film in the previous operation.

The timing of this operation must be done with precision, such that thetwo drives operate in synchronization to eliminate any seam forming whenthe second operation is performed. Preferably, the two stations A and Bare synchronized by a Berkeley Process Control System, Series 64,manufactured and sold by Berkeley Process Control, Inc. (labelledcontrol system 100 in FIG. 1).

The first curing station A is used as the master axis and the secondstation B is controlled to register the second station in line and towind up the material. Precise machine control over all the drivemechanisms coupled with optical encoder feedback and a dedicated inpututilizing flying position measurement is essential to eliminate theseam.

Referring now to FIG. 9, the details of the block diagram of the controlsystem 100 of FIG. 1 will be explained in connection therewith. Anoptical encoder 82 coupled to the shaft 12 of drum A provides a digitalor analog electrical signal proportional to the instantaneous rotaryposition in time of Drum A. This serves as the master reference signalfor the system to which all other rotary devices are slaved.

The encoder 82 provides a homing signal in the form of a TTL(transistor-transistor-logic) square wave output in the quadrature witha differential line driver to the Berkeley axis machine controllers 401through 406. These are 64 bit RISC based machine control systems. Theyare controlled by code (programs) which is loaded from processor 410.The code is loaded into the non-volatile memory of each controller,401-406 via a serial port and cable. Once loaded, the Berkeley AxisMachines (BAM) control the process steps providing functions such assequencing, motor control, input/output, interrupts and error handling.Controller 401 is designated the master BAM. As such the homing signalfrom Drum A, 10, is input to the 0 axis position. This signal is alsosent to items 402 through 406 as the master reference signal. Thisindicates to each unit how fast the machine is operating. The functionsdirectly associated with each Drum, such as coating, laminating andstripping, are adjusted from the reference signal of each respectiveDrum, A or B. Functions which are associated with machine speed, such asunwind and rewind are coordinated from Drum A, 10.

The homing signal can be generated by a variety of types of sensors.Common types include retroreflective edge sensors, or contrast sensors.They sense a line or spot in register with each mold mounted on the DrumA or B. This homing signal will fine tune the position of Drum A or B toensure that the web is in alignment with the Drums. The registrationsensor 90, inputs directly to Drum B to ensure that Drum B in alignmentwith the striped reflective film that was produced on Drum A. Thisregistration sensor can also be an edge sensor or a reflective sensorwith a fast rise time. This sensor must be place din a region ofconstant tension to provide accurate readings. All operator interface iscontrolled via a touchscreen, now shown, utilizing menu operator screensto control the operation of the various machines, shown in FIG. 1.

Optionally, very small corner-cube prisms 202 may be formed at theleading and trailing edges of the mold plates on one of the workstations A or B. If the prism arrays 70A, 70B of the two sections areallowed to overlap slightly the resultant seam 200 created by acombination of large (L) and small (S) prisms (as shown in FIG. 6) willbe invisible at distances greater than a few feet. By creating anoverlap as shown in FIG. 6, the mold material can be applied to the moldplates with less precision and still create a seamless appearingmaterial. By "seamless appearing" is meant retroreflective sheetingwhich from a distance of about 10 feet or more appears, to the humaneye, to have no seams. Preferably the larger prisms should be formedover the smaller prisms at the section of overlap. This concept not onlyreduces the need for accurate registration but allows for stretch in thetop film.

In another alternate embodiment of the invention the tooling for themold plates is formed with small prisms S provided at the lateral edgeswhere overlap is allowed to occur and the larger prisms L are formed inthe interior (FIG. 7A).

The resultant web 210 of film 54 and prism array 70 formed in the firstcuring section A is shown in FIG. 7B while the overlap of the two webs210' (one from each section) is shown in FIG. 7C. When the overlapoccurs in the B stage of the process; the smaller prisms S of the secondstage B will be formed on top of the smaller prisms S formed in thefirst stage A.

The net result at the overlap C will be smaller prisms formed on aslightly thicker layer of material that retroreflect throughout theentire overlap area. The material boundary between the two sets of smallprisms will be substantially invisible to the unassisted human eye.

Note also that in FIG. 7C the thickness of the film plus prism array ismaintained constant except at C. Also note that the small prisms createdat the interface C will have wider observation angle performance thanthe larger prisms. This observation angle performance will cause theseam to be invisible at a distance close to the material whilemaintaining a reasonably uniform brightness at distances far from thematerial. The eye will not perceive a seam to be present at near or fardistances. At long or far distances the eye cannot resolve the areawhere the overlap occurs. At short distances the eye will see uniformbrightness because the small and large prisms observation angleperformance will overlap.

In yet a further embodiment of an overlap version of the invention; thetool or mold plate 16 is provided with a tapered prism construction atthe portion which overlaps (See FIG. 8A). This can be accomplished byfly-cutting or grinding the uniform size prisms of the mold along thedotted line x--x. The resultant material formed with the tool of FIG. 8Awill be shaped as shown in FIG. 8B with prisms P of decreasing height atthe lateral edges. When two such tapered tools are used to form theretroreflective sheeting 300 with an overlap at C the material willappear as shown in FIG. 8C which will also appear to be seamless to thenaked eye.

Although the mold plates 16 may be formed from a synthetic resin, thepreferred mold plate has a metallic surface to ensure a very smooth,precise surface on the cube-corner faces and to minimize the likelihoodof deterioration during extensive use, as well as of possible adhesionbetween the molding materials and the surface of the mold. Accordingly,the mold may be fabricated directly from a suitable metal by engraving,bobbing or otherwise forming the cube-corner recesses therein.Alternatively, a suitably engraved or otherwise formed metallic membermay be used as a master mold for forming the desired mold element by thedeposition of metal thereon to form a layer of sufficient thicknesswhich is then stripped therefrom. These stripped impressions which maybe made by conventional electroforming procedures are then used as themold elements after mounting upon a suitable support surface to avoidinjury thereto and the mold surface may then be developed on a suitablesupport member from a multiplicity of such elements. In order tominimize corrosion of the metallic surfaces of the mold plates, it hasbeen found desirable to provide a highly inert metallic coating thereonsuch as may be obtained by depositing gold or a gold alloy thereon.

As illustrated, the support for the mold surface is most desirablyprovided by a rotatably mounted drum, since such a drum facilitatescontinuous application of materials and stripping of the compositeproduct, and also provides firm support for the mold elements thereon.Other types of support members are also feasible, such as a continuousflexible belt, or a revolving disk. However, certain disadvantages suchas the non-linear configuration of the product may render the latteralternative less attractive. The means of securing the mold plates tothe drum may vary considerably depending upon the degrees of permanencyand rigidity and the heat transfer characteristics desired; for example,they may be bonded with appropriate adhesives, or they may be affixedwith suitable screws, rivets, pins or the like.

The design of the means for dispensing materials upon the moving surfaceand for stripping the composite film/prism array therefrom may also varyto a considerable degree from those of the illustrated embodiment,depending primarily upon the type of drum employed, and differentdevices appropriate for substitution will be apparent to those skilledin the art.

Flow of the molding material into the prisms recesses may be facilitatedby the prior application of a solvent, plasticizer, wetting agent orother flow promoting agent (herein collectively referred to "wettingagent"). This enhances the fluidity of the molding material about thesurfaces of the recesses and greatly promotes optimum fillage thereof.

The technique utilized for achieving solidification of the moldingmaterial will vary with the particular molding material selected. When amolten synthetic resin is employed as the fluid molding material,solidification may be accomplished merely by cooling thereof; this maybe accomplished through chilling of the mold, by directing cool airagainst the surface of the body member or by allowing the heat energy toradiate therefrom. When the molding material is a B-stage or partiallypolymerized resin, solidification may be accomplished by the applicationof heat for a period of time sufficient to achieve the desired degree ofpolymerization. When the molding material is a cross linkableformulation, solidification may be accomplished by promoting crosslinking of the component materials through any convenient meansdepending upon the nature of cross linkable material. As is well knownin the art, cross linking may be effected by use of free radicalinitiators, heat, high energy radiation and the link, and the radiatingelements depicted in the drawings may therefore comprise any suitablesource of energy. Thus, they may be a simple infra-red or other heatsource, a source of alpha or beta particles, gamma or X-ray radiation,photons, etc. Moreover, it will be appreciated that the molding materialmay be essentially monomeric in character and that the solidificationthereof may be accomplished by polymerization in situ within thecube-corner recesses of the mold surface; such polymerization may bepromoted by heat, free radical initiators, or high energy radiation, andthe actinic source may be internal for the support member if so desired.In still another technique, a plastisol formulation may be employed inwhich the resin if fluxed by the plasticizer upon the application ofheat. Obviously, combinations of these techniques also may be used toobtain the desired solidification.

Various synthetic resins may be employed for the cube-cornerformulations and for the sheet material including polymers of (alk)acrylic acid esters such as polymethyl methacrylate and polybutylacrylate; cellulose esters such as cellulose acetate polymer, celluloseacetate/butyrate copolymer, and cellulose propionate polymer; vinylhalides such as polyvinyl fluoride; vinylidene halides such aspolyvinylidene chloride; monovinylidene aromatic hydrocarbon polymerssuch as polystyrene and styrene/acrylonitrile copolymers; ethylenicallyunsaturated nitriles such as polyacrylonitrile; polycarbonates;polyesters such as polyethylene terephthalate; polyphenylene oxide;polysulfones; and polyolefins such as polyethylene and polypropylene.Interpolymers of various of the several above-mentioned types ofmonomers, e.g., vinyl chloride/vinyl acetate copolymers, may also beemployed, as may be mixtures of polymers. The particular resinformulations selected for the components of the composite structure willvary depending upon the application, the thickness desired for the bodymember, the desire for flexibility, and the need for achievinginteradhesion therebetween. For outdoor applications, materials whichare moisture resistant, ultraviolet resistant and abrasion resistant areparticularly advantageously employed at least for the body portion sincethat portion is generally exposed to the atmosphere and requires goodweathering characteristics. Moreover, it will be appreciated that thesheet material may itself be a laminate of films or sheets of twodifferent synthetic resins, and it may be provided with coatings ofappropriate materials.

The resins preferably employed for the body portion include polyvinylhalide, polyethylene terephthalate, polyvinylidene chloride,polycarbonates, polysulfones and cellulose ester polymers. The resinspreferably employed for the cube-corner formations comprise (alk)acrylic acid ester resins, acrylic-modified vinyl chloride resins, vinylchloride/vinyl acetate copolymers, ethylenically unsaturated nitrileresins, monovinylidene aromatic hydrocarbon resins, olefin resins,cellulose ester resins, polysulfone resins, polyphenylene oxide resinsand polycarbonates. Exemplary combinations for the bodyportion/cube-corner formations include polyvinyl chloride/acrylicmodified polyvinyl chloride; polyvinyl fluoride/polyvinyl chloride;polycarbonate/polycarbonate; polyvinyl chloride/polymethyl methacrylate;polysulfone/polymethyl methacrylate; polysulfone/polyvinyl chloride; andpolyethylene terephthalate/polymethyl methacrylate.

In selecting the molding materials employed for the present invention,it should be remembered that long lasting properties will require resinswhich do not have readily volatilizable plasticizers or othercomponents, and which have an acceptable level of light stability. Thus,stabilized formulations are desirably employed when the resin itself issusceptible to light or oxygen degradation. By proper selection of theresin systems, the sheet material amy also provide a valuable degree ofprotection for the resin of the cube-corner formations, which mayexhibit relatively poor stability when the cube-corner formation areselectively coated and further coated with a lacquer and/or adhesive.These coatings also may act as protective layers since the body portionswill, in many applications, serve as a barrier layer for ultravioletradiation, vapor, gasses, etc. Moreover, the sheet materials isdesirably fabricated of a resin which affords a high degree of abrasionresistance since aberrations in the front surface of the compositestructure will greatly reduce its retroreflectivity.

It will be readily appreciated that the cube-corner formations must havesmooth faces and that the intersecting faces thereof should provideessentially perfect cube-corners. Any deviation from a perfectcube-corner or surface irregularity will materially reduce theretroreflectivity of the formation, and is desirable only under certaincontrolled circumstances.

Normally, the air interface at the cube-corner formations will be reliedupon for retroreflection of the light rays. Obviously, the angle atwhich the light rays strike the faces of the cube-corners will determinewhether each ray is retroreflected or passes outwardly through the rearsurface. If the angle of incidence is less than the critical angle forthe prism material employed, the light ray will not be retroreflected.However, the predominant portion of light rays entering the frontsurface of the sheet material will be retroreflected by the cube-cornerformations.

The reflectivity of the cube-corner formations can be enhanced bydepositing a reflective coating thereon. Such a coating may beconveniently provided by a metallizing technique such as that wherein avery thin film of aluminum or other metal is deposited on the surface byvaporization thereof at a very low subatmospheric pressure; chemicaldeposition techniques may also be used. Reflective coatings may also beprovided by use of a lacquer containing metallic particles of pigmentsaffording high degrees of reflectivity; for example, pearl lacquers maybe employed. In still another technique, the reflective coating may beprovided by a metallized synthetic plastic film applied in intimatecontact over the surface of the cube-corner formations.

Although the cube-corner formations in the illustrated embodiment have auniform orientation within the array, it is possible to employ a patternin which certain of the cube-corner formations are disposed in such amanner that their faces are not parallel to any of the faces of theadjacent cube-corner formations. Moreover, certain of the cube-cornerformations may be disposed with their apices aligned other thanvertically over the center of their respective bases. By thus tippingsome of the cube-corner formations, retroreflectivity over a broaderangle is provided for-certain applications, while maximum reflectivityis diminished. This is desirable for certain applications; for example,highway signs desirably may exhibit retroreflection over a broader anglerelative to the surface of the sign and some light scattering desirablymay be provided although the light rays falling thereon may beessentially perpendicular to its face.

By use of a sheet material of a relatively flexible resin, the compositestructure may be readily shaped to various support surfaces, such as thecorners of buildings, the contour of hand rails, etc. Moreover, sincethe composite structure may be very thin, seamless appearing, and highlyflexible, it may be readily applied to fabrics used as garments, or itmay itself be used in such a manner, thus affording a great deal ofnight-time visibility to the wearer. Exemplary uses for safetyapplications are tabs and stripes on jackets and rainwear, tags that maybe worn at various points upon the body, reflective patches for hats,reflective welting for the production of various garments, etc.

Equivalents

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to specificembodiments of the invention described specifically herein. Suchequivalents are intended to be encompassed in the scope of the followingclaims.

We claim:
 1. Apparatus for forming retroreflective sheeting formed of afilm upon which a seamless array of prisms is joined, said apparatuscomprising at least two mold surfaces, each surface containing areas ofarrays of prismatic recesses and areas of blank spaces, said apparatusincluding:a first applicator for applying a prism forming material to afirst such mold surface to fill the recesses with said material; a firstmechanism for transferring the material to the film to form areas ofarrays of prisms on said film leaving areas of blank spaces on saidfilm; a second applicator for applying said prism forming material to asecond such mold surface to fill the recesses in the second mold surfacewith said material; and a second mechanism for transferring the materialin the recesses of the second mold surface onto the areas of blankspaces in the film in such a manner as to form a seamless continuousfilm of retroreflective sheeting.
 2. The apparatus of claim 1 whereinthe mold surfaces are provided on the periphery of rotatable drums andthe film is transported over the drums.
 3. The apparatus of claim 1wherein the prismatic recesses in the first mold surface differ in sizefrom those in the second mold surface and the area of the arrays ofprisms in the first mold surface is larger than the area of the arraysof prisms in the second mold surface such that an overlap occurstherebetween.
 4. The apparatus of claim 1 wherein the areas of thespaces and areas of arrays on said mold surfaces are substantially equaland are alternately spaced over each of the mold surfaces.
 5. Theapparatus of claim 1 wherein sections of the arrays of prismaticrecesses adjacent the edges thereof are tapered in height.